Method of an uplink harq operation at an expiry of time alignment timer

ABSTRACT

A method of performing a Hybrid Automatic Repeat reQuest (HARQ) operation in a wireless communication system. The method according to one embodiment includes storing a data unit into at least one of a HARQ buffer among all HARQ buffers; and flushing all HARQ buffers when a timer expires. The timer is a time alignment timer (TAT) which is used to control how long a User Equipment (UE) is considered to have an uplink time that is aligned. The stored data unit is a Medium Access Control (MAC) Protocol Data Unit (PDU). The TAT is started when a time advance command (TAC) is received from a network.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of co-pending U.S. patent applicationSer. No. 14/448,701 filed on Jul. 31, 2014, which is a Continuation ofU.S. patent application Ser. No. 13/645,302 filed on Oct. 4, 2012 (nowU.S. Pat. No. 8,812,925, issued on Aug. 19, 2014), which is aContinuation of U.S. patent application Ser. No. 12/363,263 filed onJan. 30, 2009 (now U.S. Pat. No. 8,312,336, issued on Nov. 13, 2012),which claims priority to Korean Patent Application No. 10-2009-0007145filed on Jan. 29, 2009, and which also claims priority to U.S.Provisional Application Nos. 61/025,311 filed on Feb. 1, 2008 and61/087,153 filed on Aug. 7, 2008. The entire contents of all of theabove applications are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radio (wireless) communication systemproviding a radio communication service and a mobile terminal, and moreparticularly, to a method of an uplink HARQ operation of the mobileterminal in an Evolved Universal Mobile Telecommunications System(E-UMTS) or a Long Term Evolution (LTE) system.

2. Discussion of the Related Art

FIG. 1 shows an exemplary network structure of an Evolved UniversalMobile Telecommunications System (E-UMTS) as a mobile communicationsystem to which a related art and the present invention are applied. TheE-UMTS system is a system that has evolved from the existing UMTSsystem, and its standardization work is currently being performed by the3GPP standards organization. The E-UMTS system can also be referred toas a LTE (Long-Term Evolution) system.

The E-UMTS network can roughly be divided into an E-UTRAN and a CoreNetwork (CN). The E-UTRAN generally comprises a terminal (i.e., UserEquipment (UE)), a base station (i.e., eNode B), an Access Gateway (AG)that is located at an end of the E-UMTS network and connects with one ormore external networks. The AG may be divided into a part for processinguser traffic and a part for handling control traffic. Here, an AG forprocessing new user traffic and an AG for processing control traffic canbe communicated with each other by using a new interface. One eNode Bmay have one or more cells. An interface for transmitting the usertraffic or the control traffic may be used among the eNode Bs. The CNmay comprise an AG, nodes for user registration of other UEs, and thelike. An interface may be used to distinguish the E-UTRAN and the CNfrom each other.

The various layers of the radio interface protocol between the mobileterminal and the network may be divided into a layer 1 (L1), a layer 2(L2) and a layer 3 (L3), based upon the lower three layers of the OpenSystem Interconnection (OSI) standard model that is well-known in thefield of communications systems. Among these layers, Layer 1 (L1),namely, the physical layer, provides an information transfer service toan upper layer by using a physical channel, while a Radio ResourceControl (RRC) layer located in the lowermost portion of the Layer 3 (L3)performs the function of controlling radio resources between theterminal and the network. To do so, the RRC layer exchanges RRC messagesbetween the terminal and the network. The RRC layer may be located bybeing distributed in network nodes such as the eNode B, the AG, and thelike, or may be located only in the eNode B or the AG.

FIG. 2 shows exemplary control plane architecture of a radio interfaceprotocol between a terminal and a UTRAN (UMTS Terrestrial Radio AccessNetwork) according to the 3GPP radio access network standard. The radiointerface protocol as shown in FIG. 2 is horizontally comprised of aphysical layer, a data link layer, and a network layer, and verticallycomprised of a user plane for transmitting user data and a control planefor transferring control signaling. The protocol layer in FIG. 2 may bedivided into L1 (Layer 1), L2 (Layer 2), and L3 (Layer 3) based upon thelower three layers of the Open System Interconnection (OSI) standardsmodel that is widely known in the field of communication systems.

Hereinafter, particular layers of the radio protocol control plane ofFIG. 2 and of the radio protocol user plane of FIG. 3 will be describedbelow.

The physical layer (Layer 1) uses a physical channel to provide aninformation transfer service to a higher layer. The physical layer isconnected with a medium access control (MAC) layer located thereabovevia a transport channel, and data is transferred between the physicallayer and the MAC layer via the transport channel. Also, betweenrespectively different physical layers, namely, between the respectivephysical layers of the transmitting side (transmitter) and the receivingside (receiver), data is transferred via a physical channel.

The Medium Access Control (MAC) layer of Layer 2 provides services to aradio link control (RLC) layer (which is a higher layer) via a logicalchannel. The RLC layer of Layer 2 supports the transmission of data withreliability. It should be noted that if the RLC functions areimplemented in and performed by the MAC layer, the RLC layer itself maynot need to exist. The PDCP layer of Layer 2 performs a headercompression function that reduces unnecessary control information suchthat data being transmitted by employing Internet Protocol (IP) packets,such as IPv4 or IPv6, can be efficiently sent over a radio interfacethat has a relatively small bandwidth.

The Radio Resource Control (RRC) layer located at the lowermost portionof Layer 3 is only defined in the control plane, and handles the controlof logical channels, transport channels, and physical channels withrespect to the configuration, re-configuration and release of radiobearers (RB). Here, the RB refers to a service that is provided by Layer2 for data transfer between the mobile terminal and the UTRAN.

As for channels used in downlink transmission for transmitting data fromthe network to the mobile terminal, there is a Broadcast Channel (BCH)used for transmitting system information, and a downlink Shared Channel(SCH) used for transmitting user traffic or control messages. A downlinkmulticast, traffic of broadcast service or control messages may betransmitted via the downlink SCH or via a separate downlink MulticastChannel (MCH). As for channels used in uplink transmission fortransmitting data from the mobile terminal to the network, there is aRandom Access Channel (RACH) used for transmitting an initial controlmessage, and an uplink Shared Channel (SCH) used for transmitting usertraffic or control messages.

As for downlink physical channels for transmitting informationtransferred via the channels used in downlink transmission over a radiointerface between the network and the terminal, there is a PhysicalBroadcast Channel (PBCH) for transmitting BCH information, a PhysicalMulticast Channel (PMCH) for transmitting MCH information, a PhysicalDownlink Shared Channel (PDSCH) for transmitting PCH and a downlink SCHinformation, and a Physical Downlink Control Channel (PDCCH) (also,referred to as ‘DL L1/L2 control channel’) for transmitting controlinformation provided by the first and second layers such as a DL/ULScheduling Grant, and the like. As for uplink physical channels fortransmitting information transferred via the channels used in uplinktransmission over a radio interface between the network and theterminal, there is a Physical Uplink Shared Channel (PUSCH) fortransmitting uplink SCH information, a Physical Random Access Channel(PRACH) for transmitting RACH information, and a Physical Uplink ControlChannel (PUCCH) for transmitting control information provided by thefirst and second layers, such as a HARQ ACK or NACK, a SchedulingRequest (SR), a Channel Quality Indicator (CQI) report, and the like.

In LTE system, a HARQ operation is performed in a MAC (Medium AccessControl) layer for an effective data transmission. The following is adetailed description of the HARQ operation.

FIG. 4 is an exemplary view showing a HARQ operation method for aneffective data transmission. As illustrated in FIG. 4, a base station(or eNB) may transmit downlink scheduling information (referred as ‘DLscheduling information’ hereafter) through a PDCCH (Physical DownlinkControl Channel) in order to provide data to a terminal (UE) during aHARQ operation. The DL scheduling information may include a UEidentifier (UE ID), a UE group identifier (Group ID), an allocated radioresource assignment, a duration of the allocated radio resourceassignment, a transmission parameter (e.g., Modulation method, payloadsize, MIMO related information, etc), HARQ process information, aredundancy version, or a new data indicator (NID), etc. Usually, theterminal (UE) performs multiple HARQ processes, the multiple HARQprocesses are operated synchronously. Namely, each HARQ process isallocated synchronously in every transmission time interval (TTI). Forexample, a HARQ process 1 may perform in a first transmission timeinterval (TTI 1), a HARQ process 2 may perform in TTI 2, . . . , a HARQprocess 8 may perform in TTI 8, the HARQ process 1 may again perform inTTI 9, and the HARQ process 2 may again perform in TTI 10, etc. Sincethe HARQ processes are allocated in synchronous manner, a certain HARQprocess associated with a TTI which receives a PDCCH for initialtransmission of a particular data may be used for such datatransmission. For example, if the terminal receives a PDCCH including anuplink scheduling information in Nth TTI, the terminal may actuallytransmit a data in N+4 TTI.

The HARQ retransmission of the terminal is operated in a non-adaptivemanner. That is, an initial transmission of a particular data ispossible only when the terminal receives a PDCCH including an uplinkscheduling information. However, the HARQ retransmission of the data canbe possibly operated without receiving the PDCCH, as next TTI allocatedto a corresponding HARQ process can be used with same uplink schedulinginformation. Here, transmission parameters may be transmitted through acontrol channel such as a PDCCH, and these parameters may be varied witha channel conditions or circumstances. For example, if a current channelcondition is better than a channel condition of an initial transmission,higher bit rate may be used by manipulating a modulation scheme or apayload size. In contrast, if a current channel condition is worst thana channel condition of an initial transmission, lower bit rate may beused.

The terminal checks an uplink scheduling information by monitoring aPDCCH in every TTI. Then, the terminal transmits data through a PUSCHbased on the uplink scheduling information. The terminal firstlygenerates the data in a MAC PDU format, and then stores it in a HARQbuffer. After that, the terminal transmits the data based on the uplinkscheduling information. Later, the terminal waits to receive a HARQfeedback from a base station (eNB). If the terminal receives a HARQ NACKfrom the base station in response to the transmitted data, the terminalretransmits the data in a retransmission TTI of a corresponding HARQprocess. If the terminal receives a HARQ ACK from the base station inresponse to the transmitted data, the terminal terminates to operate theretransmission of the HARQ. The terminal counts a number oftransmissions (i.e. CURRENT_TX_NB) whenever the data is transmitted in aHARQ process. If the number of transmissions is reached to a maximumnumber of transmissions, which set by an upper layer, data in the HARQbuffer is flushed.

The HARQ retransmission is performed according to a HARQ feedback from abase station, a data existence in the HARQ buffer, or a transmissiontime of a corresponding HARQ process. Here, each of HARQ process mayhave a HARQ buffer respectively. The value in the NDI (New DataIndicator) field contained in the PDCCH may be used for the UE todetermine whether the received data is an initial transmission data or aretransmitted data. More specifically, the NDI field is 1 bit field thattoggles every time a new data is transmitted or received. (0->1->0->1->. . . ) As such, the value in the NDI for the retransmitted data alwayshas a same value used in an initial transmission. From this, the UE mayknow an existence of retransmitted data by comparing these values.

Description of an uplink timing alignment maintenance in a LTE systemwill be given. In the LTE system that based on an Orthogonal FrequencyDivision Multiplex (OFDM) technology, there is possibility ofinterferences between terminals (UEs) during a communication between UEand base station (eNB). In order to minimize interferences betweenterminals, it is important that the base station must manage or handle atransmission timing of the UE. More particularly, the terminal may existin random area within a cell, and this implies that a data transmissiontime (i.e., traveling time of data from UE to base station) can bevaried based on a location of the terminal. Namely, if the terminal iscamped on edge of the cell, data transmission time of this specificterminal will be much longer than data transmission time of thoseterminals who camped on a center of the cell. In contrast, if theterminal is camped on the center of the cell, data transmission time ofthis specific terminal will be much shorter than data transmission timeof those terminals who camped on the edge of the cell. The base station(eNB) must manage or handle all data or signals, which are transmittedby the terminals within the cell, in order to prevent the interferencesbetween the terminals. Namely, the base station must adjust or manage atransmission timing of the terminals upon each terminal's condition, andsuch adjustment can be called as the timing alignment maintenance. Oneof the methods for maintaining the timing alignment is a random accessprocedure. Namely, during the random access procedure, the base stationreceives a random access preamble transmitted from the terminal, and thebase station can calculate a time alignment (Sync) value using thereceived random access preamble, where the time alignment value is toadjust (i.e., faster or slower) a data transmission timing of theterminal. The calculated time alignment value can be notified to theterminal by a random access response, and the terminal can update thedata transmission timing based on the calculated time alignment value.In other method, the base station may receive a sounding referencesymbol (SRS) transmitted from the terminal periodically or randomly, thebase station may calculate the time alignment (Sync) value based on theSRS, and the terminal may update the data transmission timing accordingto the calculated time alignment value.

As explained above, the base station (eNB) may measure a transmissiontiming of the terminal though a random access preamble or SRS, and maynotify an adjustable timing value to the terminal. Here, the timealignment (Sync) value (i.e., the adjustable timing value) can be calledas a time advance command (referred as ‘TAC’ hereafter). The TAC may beprocess in a MAC (Medium Access control) layer. Since the terminal doesnot camps on a fixed location, the transmission timing is frequentlychanged based on a terminal's moving location and/or a terminal's movingvelocity. Concerning with this, if the terminal receives the timeadvance command (TAC) from the base station, the terminal expect thatthe time advance command is only valid for certain time duration. A timealignment timer (TAT) is used for indicating or representing the certaintime duration. As such, the time alignment timer (TAT) is started whenthe terminal receives the TAC (time advance command) from the basestation. The TAT value is transmitted to the terminal (UE) through a RRC(Radio Resource Control) signal such as system information (SI) or aradio bearer reconfiguration. Also, if the terminal receives a new TACfrom the base station during an operation of the TAT, the TAT isrestarted. Further, the terminal does not transmit any other uplink dataor control signal (e.g., data on physical uplink shared channel (PUSCH),control signal on Physical uplink control channel (PUCCH)) except forthe random access preamble when the TAT is expired or not running.

In general, a MAC layer of the terminal and base station handles a timealignment (synchronize) management. Namely, The TAC is generated in theMAC layer of the base station, and the MAC layer of the terminalreceives the TAC through a MAC message from the base station. However,because the TAC is received by the MAC message, a transmission of theTAC is not fully guaranteed. For example, the base station transmits theMAC message including the TAC in a HARQ process, and the terminalattempts to receive the data. The terminal transmits a NACK signal tothe base station if the terminal fails to decode the data. However, ifsuch NACK signal is mistakenly treated as an ACK signal by the basestation, a TAT of the base station is restarted whereas a TAT of theterminal is not restarted. Thusly, a failed synchronization can behappened between the terminal and base station.

Another example of drawback in a related art can be given as following.Firstly, the terminal receives an uplink scheduling information througha PDCCH for a transmission of data 1. Then, the terminal transmits thedata 1 to the base station using the HARQ process. In response to thetransmitted data 1, the terminal receives a NACK from the base station.Therefore the terminal has to retransmit the data 1, however, the TAT ofthe terminal can be expired before a retransmission of the data 1. Inthis situation, the terminal can not possibly retransmit the data 1 dueto expiry of the TAT. Therefore, the terminal restarts the TAT afterreceiving a TAC from the base station though a random access channel(RACH) procedure. However, the terminal still transmits data 1 at atransmission timing of the HARQ process because the data 1 is stillstored in a HARQ buffer of the terminal. In this case, the transmissionof the data 1 is not expected by the base station, this datatransmission can be collided with other data transmission by otherterminals.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a method ofprocessing data for a HARQ (Hybrid Automatic Repeat reQuest) in awireless communication system, and more particularly, for an optimizeduplink HARQ operation when time alignment timer is not running or at anexpiry of time alignment timer.

To achieve this and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described herein,there is provided a method of processing data for a HARQ (HybridAutomatic Repeat Request) operation in a wireless communication system,the method comprising: receiving an uplink Grant from a network;generating a data unit based on the received uplink grant; storing thegenerated data unit into a plurality of buffers; and flushing the storeddata unit in the plurality of buffers when a timer expires.

Also, To achieve this and other advantages and in accordance with thepurpose of the present invention, as embodied and broadly describedherein, there is also provided a method of processing data for a HARQ(Hybrid Automatic Repeat Request) operation in a wireless communicationsystem, the method comprising: receiving an uplink Grant from a network;generating a data unit based on the received uplink grant; storing thegenerated data unit into a plurality of buffers; and flushing the storeddata in the plurality of buffers when the timer is not running.

Also, To achieve this and other advantages and in accordance with thepurpose of the present invention, as embodied and broadly describedherein, there is also provided a method of processing data for a HARQ(Hybrid Automatic Repeat Request) operation in a wireless communicationsystem, the method comprising: receiving an uplink Grant from a network;generating a data unit based on the received uplink grant; storing thegenerated data unit into a plurality of buffers; determining whether ornot a timer is running; determining whether a command for starting thetimer is received; and flushing the stored data in the plurality ofbuffers when it is determined that the timer is not running and thecommand is received.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary network structure of an Evolved UniversalMobile Telecommunications System (E-UMTS) as a mobile communicationsystem to which a related art and the present invention are applied;

FIG. 2 shows an exemplary view of related art control plane architectureof a radio interface protocol between a terminal and an E-UTRAN;

FIG. 3 shows an exemplary view of related art user plane architecture ofa radio interface protocol between a terminal and an E-UTRAN;

FIG. 4 is an exemplary view showing a HARQ operation method for aneffective data transmission;

FIG. 5 shows an exemplary view of a contention based random accessprocedure;

FIG. 6 shows an exemplary view of a non-contention based random accessprocedure;

FIG. 7 shows an exemplary view of flushing data in HARQ buffer at anexpiry of time alignment timer (TAT) according to the present invention;

FIG. 8 shows an exemplary view of flushing data in HARQ buffer when atime alignment timer (TAT) is not running according to the presentinvention; and

FIG. 9 shows an exemplary view of flushing data in HARQ buffer byreceiving a new timing advance command (TAC) when a time alignment timer(TAT) is not running according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

One aspect of this disclosure relates to the recognition by the presentinventors about the problems of the related art as described above, andfurther explained hereafter. Based upon this recognition, the featuresof this disclosure have been developed.

Although this disclosure is shown to be implemented in a mobilecommunication system, such as a UMTS developed under 3GPPspecifications, this disclosure may also be applied to othercommunication systems operating in conformity with different standardsand specifications.

Hereinafter, description of structures and operations of the preferredembodiments according to the present invention will be given withreference to the accompanying drawings.

In general, a terminal (or UE) may perform a random access procedure inthe following cases: 1) when the terminal performs an initial accessbecause there is no RRC Connection with a base station (or eNB), 2) whenthe terminal initially accesses to a target cell in a handoverprocedure, 3) when it is requested by a command of a base station, 4)when there is uplink data transmission in a situation where uplink timesynchronization is not aligned or where a specific radio resource usedfor requesting radio resources is not allocated, and 5) when a recoveryprocedure is performed in case of a radio link failure or a handoverfailure.

In the LTE system, the base station allocates a dedicated random accesspreamble to a specific terminal, and the terminal performs anon-contention random access procedure which performs a random accessprocedure with the random access preamble. In other words, there are twoprocedures in selecting the random access preamble: one is a contentionbased random access procedure in which the terminal randomly selects onewithin a specific group for use, another is a non-contention basedrandom access procedure in which the terminal uses a random accesspreamble allocated only to a specific terminal by the base station. Thedifference between the two random access procedures is that whether ornot a collision problem due to contention occurs, as described later.And, the non-contention based random access procedure may be used, asdescribed above, only in the handover procedure or when it is requestedby the command of the base station.

Based on the above description, FIG. 5 shows an operation procedurebetween a terminal and a base station in a contention based randomaccess procedure.

First, a terminal in the contention based random access randomly mayselect a random access preamble within a group of random accesspreambles indicated through system information or a handover command,may select PRACH resources capable of transmitting the random accesspreamble, and then may transmit the selected random access preamble to abase station (Step 1).

After transmitting the random access preamble, the terminal may attemptto receive a response with respect to its random access preamble withina random access response reception window indicated through the systeminformation or the handover command (Step 2). More specifically, therandom access response information is transmitted in a form of MAC PDU,and the MAC PDU may be transferred on the Physical Downlink SharedChannel (PDSCH). In addition, the Physical Downlink Control Channel(PDCCH) is also transferred such that the terminal appropriatelyreceives information transferred on the PDSCH. That is, the PDCCH mayinclude information about a terminal that should receive the PDSCH,frequency and time information of radio resources of the PDSCH, atransfer format of the PDSCH, and the like. Here, if the PDCCH has beensuccessfully received, the terminal may appropriately receive the randomaccess response transmitted on the PDSCH according to information of thePDCCH. The random access response may include a random access preambleidentifier (ID), an UL Grant, a temporary C-RNTI, a Time AlignmentCommand, and the like. Here, the random access preamble identifier isincluded in the random access response in order to notify terminals towhich information such as the UL Grant, the temporary C-RNTI, and theTime Alignment Command would be valid (available, effective) because onerandom access response may include random access response informationfor one or more terminals. Here, the random access preamble identifiermay be identical to the random access preamble selected by the terminalin Step 1.

If the terminal has received the random access response valid to theterminal itself, the terminal may process each of the informationincluded in the random access response. That is, the terminal appliesthe Time Alignment Command, and stores the temporary C-RNTI. Inaddition, the terminal uses the UL Grant so as to transmit data storedin a buffer of the terminal or newly generated data to the base station(Step 3). Here, a terminal identifier should be essentially included inthe data which is included in the UL Grant (message 3). This is because,in the contention based random access procedure, the base station maynot determine which terminals are performing the random accessprocedure, but later the terminals should be identified for contentionresolution. Here, two different schemes may be provided to include theterminal identifier. A first scheme is to transmit the terminal's cellidentifier through the UL Grant if the terminal has already received avalid cell identifier allocated in a corresponding cell prior to therandom access procedure. Conversely, the second scheme is to transmitthe terminal's unique identifier (e.g., S-TMSI or random ID) if theterminal has not received a valid cell identifier prior to the randomaccess procedure. In general, the unique identifier is longer than thecell identifier. In Step 3, if the terminal has transmitted data throughthe UL Grant, the terminal starts the contention resolution timer.

After transmitting the data with its identifier through the UL Grantincluded in the random access response, the terminal waits for anindication (instruction) of the base station for the contentionresolution. That is, the terminal attempts to receive the PDCCH so as toreceive a specific message (Step 4). Here, there are two schemes toreceive the PDCCH. As described above, if the terminal identifiertransmitted via the UL Grant is the cell identifier, the terminalattempts to receive the PDCCH by using its own cell identifier. If theterminal identifier transmitted via the UL Grant is its uniqueidentifier, the terminal attempts to receive the PDCCH by using thetemporary C-RNTI included in the random access response. Thereafter, forthe former, if the PDCCH (message 4) is received through its cellidentifier before the contention resolution timer is expired, theterminal determines that the random access procedure has beensuccessfully (normally) performed, thus to complete the random accessprocedure. For the latter, if the PDCCH is received through thetemporary cell identifier before the contention resolution timer isexpired, the terminal checks data (message 4) transferred by the PDSCHthat the PDCCH indicates. If the unique identifier of the terminal isincluded in the data, the terminal determines that the random accessprocedure has been successfully (normally) performed, thus to completethe random access procedure.

FIG. 6 shows an operation procedure between a terminal and a basestation in a non-contention based random access procedure. As comparedwith the contention based random access procedure, the random accessprocedure is determined to be successfully performed by receiving therandom access response information in the non-contention based randomaccess procedure, thus to complete the random access process.

In general, the non-contention based random access procedure may beperformed in the following two cases: one is the handover procedure, andthe other is a request by the command of the base station. To becertain, the contention based random access procedure may also beperformed in those two cases. First, for the non-contention based randomaccess procedure, it is important to receive, from the base station, adedicated random access preamble without having any possibility ofcontention. Here, a handover command and a PDCCH command may be used toassign the random access preamble. Then, after the random accesspreamble dedicated to only the terminal itself has been assigned fromthe base station, the terminal transmits the preamble to the basestation. Thereafter, the method for receiving the random access responseinformation is the same as that in the above-described contention basedrandom access procedure.

As aforementioned in this disclosure, the present invention proposes amethod of flushing data in all HARQ buffer of the terminal when a timealignment timer (TAT) is not running or is expired.

FIG. 7 shows an exemplary view of flushing data in HARQ buffer at anexpiry of time alignment timer (TAT) according to the present invention.As illustrated in FIG. 7, the present invention proposes to flush allHARQ buffers at the TAT expiry. More detailed description of FIG. 7 willbe given as following. First, the terminal may receive a PDCCH (PhysicalDownlink Control Channel) including an uplink scheduling information(i.e. UL grant) for a data transmission of an uplink. Here, the PDCCHmay include a C-RNTI (Cell-Radio Network Temporary Identifier) orSemi-Persistent Scheduling C-RNTI (SPS C-RNTI). Thereafter, the terminalmay generate a MAC PDU (referred as MAC PDU-1 hereafter) according tothe received uplink scheduling information, and may store the generatedMAC PDU-1 in a corresponding HARQ buffer. Further, the terminal maytransmit the stored MAC PDU-1 to the base station at a transmissiontiming of a corresponding HARQ process. After the MAC PDU-1 istransmitted, the terminal may wait to receive a HARQ feedback from thebase station. At this moment, the time alignment timer (TAT) of theterminal may expire. According to the present invention, the terminalmay flush data in all HARQ buffers including a HARQ buffer having theMAC PDU-1 at the time of TAT expiry.

FIG. 8 shows an exemplary view of flushing data in HARQ buffer when atime alignment timer (TAT) is not running according to the presentinvention. As illustrated in FIG. 8, the present invention proposes toflush all HARQ buffers when the TAT is not running. More detaileddescription of FIG. 8 will be given as following. After the TAT isexpired, the terminal may flush data in all HARQ buffers. Here, acurrent TAT of the terminal is not running and there is no data in allHARQ buffers. In this case, the terminal may further receive a PDCCHincluding an uplink scheduling information for an uplink datatransmission. Here, the PDCCH may include a C-RNTI (Cell-Radio NetworkTemporary Identifier) or Semi-Persistent Scheduling C-RNTI (SPS C-RNTI).Thereafter, the terminal may generate a MAC PDU (referred as MAC PDU-2hereafter) according to the received uplink scheduling information, andmay store the generated MAC PDU-2 in a corresponding HARQ buffer.However, according to the present invention, the terminal may flush datain all HARQ because the TAT of the terminal is not running.

FIG. 9 shows an exemplary view of flushing data in HARQ buffer byreceiving a new timing advance command (TAC) when a time alignment timer(TAT) is not running according to the present invention. As illustratedin FIG. 9, the present invention proposes to flush all HARQ buffers whenthe terminal receives a new TAC while a TAT of the terminal is notrunning after its expiration. More detailed description of FIG. 9 willbe given as following. After the TAT is expired, the terminal may flushdata in all HARQ buffers. While the TAT is not running, the terminal mayfurther receive a PDCCH including an uplink scheduling information foran uplink data transmission. Here, the PDCCH may include a C-RNTI(Cell-Radio Network Temporary Identifier) or Semi-Persistent SchedulingC-RNTI (SPS C-RNTI). Thereafter, the terminal may generate a MAC PDU(referred as MAC PDU-3 hereafter) according to the received uplinkscheduling information, and may store the generated MAC PDU-3 in acorresponding HARQ buffer. The terminal may attempt to transmit the MACPDU-3 to the base station. However, since the TAT is not running, theterminal may not transmit the MACE PDU-3. Here, the MAC PDU-3 is kept inthe corresponding HARQ buffer. At this moment, the terminal may receivea new TAC. For example, the terminal may receive the new TAC by a randomaccess response during the random access channel (RACH) procedure. Oncethe new TAC is received by the terminal, the terminal may flush data inall HARQ buffer and may restart the TAT.

According to the present invention, when the time alignment timerexpires, all HARQ buffers (i.e., all uplink HARQ buffers) are flushedand the next transmission for each process is considered as the veryfirst transmission. Namely, the terminal may notify RRC of PUCCH/SRSrelease and may clear any configured downlink assignment and uplinkgrants.

The present disclosure may provide a method of processing data for aHARQ (Hybrid Automatic Repeat Request) operation in a wirelesscommunication system, the method comprising: receiving an uplink Grantfrom a network; generating a data unit based on the received uplinkgrant; storing the generated data unit into a plurality of buffers; andflushing the stored data unit in the plurality of buffers when a timerexpires, wherein the timer is a Time Alignment Timer (TAT), the uplinkgrant is received on a PDCCH (Physical Downlink Control Channel), theuplink grant includes at least one of uplink scheduling information, aC-RNTI (Cell-Radio Network Temporary Identifier), and a Semi-persistentScheduling C-RNTI, the data unit is MAC PDU (Medium Access ControlProtocol Data Unit), and the plurality of buffers is all uplink HARQbuffers.

It can be also said that the present invention may provide a method ofprocessing data for a HARQ (Hybrid Automatic Repeat Request) operationin a wireless communication system, the method comprising: receiving anuplink Grant from a network; generating a data unit based on thereceived uplink grant; storing the generated data unit into a pluralityof buffers; and flushing the stored data in the plurality of bufferswhen the timer is not running, wherein the timer is a time Alignmenttimer (TAT), the uplink grant is received on a PDCCH (Physical DownlinkControl Channel), the uplink grant includes at least one of uplinkscheduling information, a C-RNTI (Cell-Radio Network TemporaryIdentifier), and a Semi-persistent Scheduling C-RNTI, the data unit isMAC PDU (Medium Access Control Protocol Data Unit), and the plurality ofbuffers is all uplink HARQ buffers.

Also, the present invention may provide a method of processing data fora HARQ (Hybrid Automatic Repeat Request) operation in a wirelesscommunication system, the method comprising: receiving an uplink Grantfrom a network; generating a data unit based on the received uplinkgrant; storing the generated data unit into a plurality of buffers;determining whether or not a timer is running; determining whether acommand for starting the timer is received; and flushing the stored datain the plurality of buffers when it is determined that the timer is notrunning and the command is received, wherein the command is a TimingAdvance Command (TAC).

Although the present disclosure is described in the context of mobilecommunications, the present disclosure may also be used in any wirelesscommunication systems using mobile devices, such as PDAs and laptopcomputers equipped with wireless communication capabilities (i.e.interface). Moreover, the use of certain terms to describe the presentdisclosure is not intended to limit the scope of the present disclosureto a certain type of wireless communication system. The presentdisclosure is also applicable to other wireless communication systemsusing different air interfaces and/or physical layers, for example,TDMA, CDMA, FDMA, WCDMA, OFDM, EV-DO, Wi-Max, Wi-Bro, etc.

The exemplary embodiments may be implemented as a method, apparatus orarticle of manufacture using standard programming and/or engineeringtechniques to produce software, firmware, hardware, or any combinationthereof. The term “article of manufacture” as used herein refers to codeor logic implemented in hardware logic (e.g., an integrated circuitchip, Field Programmable Gate Array (FPGA), Application SpecificIntegrated Circuit (ASIC), etc.) or a computer readable medium (e.g.,magnetic storage medium (e.g., hard disk drives, floppy disks, tape,etc.), optical storage (CD-ROMs, optical disks, etc.), volatile andnon-volatile memory devices (e.g., EEPROMs, ROMs, PROMs, RAMs, DRAMs,SRAMs, firmware, programmable logic, etc.).

Code in the computer readable medium may be accessed and executed by aprocessor. The code in which exemplary embodiments are implemented mayfurther be accessible through a transmission media or from a file serverover a network. In such cases, the article of manufacture in which thecode is implemented may comprise a transmission media, such as a networktransmission line, wireless transmission media, signals propagatingthrough space, radio waves, infrared signals, etc. Of course, thoseskilled in the art will recognize that many modifications may be made tothis configuration without departing from the scope of the presentdisclosure, and that the article of manufacture may comprise anyinformation bearing medium known in the art.

As the present disclosure may be embodied in several forms withoutdeparting from the spirit or essential characteristics thereof, itshould also be understood that the above-described embodiments are notlimited by any of the details of the foregoing description, unlessotherwise specified, but rather should be construed broadly within itsspirit and scope as defined in the appended claims, and therefore allchanges and modifications that fall within the metes and bounds of theclaims, or equivalents of such metes and bounds are therefore intendedto be embraced by the appended claims.

What is claimed is:
 1. A method of performing a Hybrid Automatic RepeatreQuest (HARQ) operation in a wireless communication system, the methodcomprising: storing a data unit into at least one of a HARQ buffer amongall HARQ buffers; and flushing all HARQ buffers when a timer expires,wherein the timer is a time alignment timer (TAT) which is used tocontrol how long a User Equipment (UE) is considered to have an uplinktime that is aligned, wherein the stored data unit is a Medium AccessControl (MAC) Protocol Data Unit (PDU), and wherein the TAT is startedwhen a time advance command (TAC) is received from a network.
 2. Themethod of claim 1, further comprising: receiving one or more uplinkgrants from the network.
 3. The method of claim 2, wherein the one ormore uplink grants are used for transmitting the data unit to thenetwork.
 4. The method of claim 1, wherein all HARQ buffers are flushedwhen the UE receives a new TAC while the TAT is not running.
 5. Themethod of claim 1, wherein all HARQ buffers are flushed when the TAT isnot running regardless of the reception of the TAC by the UE.
 6. Themethod of claim 1, wherein all HARQ buffers are flushed when the TAT isexpired regardless of the reception of the TAC by the UE.
 7. The methodof claim 1, wherein any configured downlink assignments within all HARQbuffers are also flushed when the TAT is expired.
 8. The method of claim2, wherein the one or more uplink grants are received on a PhysicalDownlink Control Channel (PDCCH).
 9. The method of claim 2, wherein theone or more uplink grants include at least one of uplink schedulinginformation, a Cell-Radio Network Temporary Identifier (C-RNTI), and aSemi-persistent Scheduling C-RNTI.
 10. The method of claim 1, wherein aRadio Resource Control (RRC) layer entity is notified to releasePhysical Uplink Control Channel/Sounding Reference Symbol (PUCCH/SRS)resources when the TAT is expired.
 11. A user equipment (UE) using aHybrid Automatic Repeat reQuest (HARQ) operation in a wirelesscommunication system, the UE comprising: a controller configured to:store a data unit into at least one of a HARQ buffer among all HARQbuffers, and flush all HARQ buffers when a timer expires, wherein thetimer is a time alignment timer (TAT) which is used to control how longthe UE is considered to have an uplink time that is aligned, wherein thestored data unit is a Medium Access Control (MAC) Protocol Data Unit(PDU), and wherein the TAT is started when a time advance command (TAC)is received from a network.
 12. The UE of claim 11, wherein thecontroller is further configured to receive one or more uplink grantsfrom the network.
 13. The UE of claim 12, wherein the one or more uplinkgrants are used for transmitting the data unit to the network.
 14. TheUE of claim 11, wherein all HARQ buffers are flushed when the UEreceives a new TAC while the TAT is not running.
 15. The UE of claim 11,wherein all HARQ buffers are flushed when the TAT is not runningregardless of the reception of the TAC.
 16. The UE of claim 11, whereinall HARQ buffers are flushed when the TAT is expired regardless of thereception of the TAC.
 17. The UE of claim 11, wherein any configureddownlink assignments within all HARQ buffers are also flushed when theTAT is expired.
 18. The UE of claim 12, wherein the one or more uplinkgrants are received on a Physical Downlink Control Channel (PDCCH). 19.The UE of claim 12, wherein the one or more uplink grants include atleast one of uplink scheduling information, a Cell-Radio NetworkTemporary Identifier (C-RNTI), and a Semi-persistent Scheduling C-RNTI.20. The UE of claim 11, wherein a Radio Resource Control (RRC) layerentity is notified to release Physical Uplink Control Channel/SoundingReference Symbol (PUCCH/SRS) resources when the TAT is expired.